1. Field of the Invention
The present invention relates to a composite material which contains a polymer chain represented by polysilane and exhibits various optical and electric characteristics, a precursor of the composite material and an optical device using the composite material.
2. Description of the Related Art
Polymers such as polysilane, polygermane and polystannane have various particular optical or electric characteristics due to a .sigma.-conjugate effect of a main chain and attract attention as materials for photoelectric devices. However, bonds of the polymer main chain, such as Si--Si, Ge--Ge and Sn--Sn are liable to be chemically denaturalize and oxidized by the irradiation of ultraviolet light with comparative ease and, therefore, they are inferior in durability. Also, they are often inferior in mechanical strength, which causes a serious problem when using as a device material.
In order to improve such an inferior durability, for example, a process for forming a three-dimensional network by reacting polar groups introduced into the polymer side chains of polysilane with each other to crosslink them is disclosed in Japanese Laid-Open Patent Publication No. 4-363327. When the three-dimensional network is formed by crosslinking as described above, the mechanical strength is increased and, at the same time, the polymer main chain is fixed in the three-dimensional network. Therefore, it becomes difficult to cause cleavage of the main chain and the chemical, thermal or optical durability is improved. However, since the crosslinking density of the conventional crosslinked material is not sufficiently high, the polymer main chain is not sufficiently fixed in the three-dimensional network and, therefore, the durability is not improved satisfactorily.
In order to improve the durability of polysilane, it is effective to form a dense three-dimensional network by enhancing the crosslinking density of the crosslinked material. As the substance for forming the three-dimensional network, for example, glass is well known. If polymers such as polysilane can be fixed in the three-dimensional network of glass through a chemical bond, a drastic improvement of the durability of the polymer is expected. In this case, it is important for improving these characteristics to mix the polymer in the glass matrix sufficiently, thereby causing no phase separation.
For example, in Japanese Laid-Open Patent Publication No. 1-183420, there has hitherto been disclosed a case wherein polysilane or polygermane is formulated in glass. This glass material was prepared by mixing a glass sol solution with nonpolar polysilane or polygermane powder or a block copolymer of a nonpolar polysilane or polygermane and a polar polysiloxane. However, when the power is mixed as described in the former case, phase separation arises as a matter of course. Even if the block copolymer is used as described in the latter case, phase separation arises, because the glass matrix is polar while the polysilane part of the copolymer is nonpolar. Therefore, the fixing effect in the three-dimensional network is inferior.
In U.S. Pat. No. 5,130,397 and Japanese Laid-Open Patent Publication No. 5-105766, there are disclosed copolymers of polymers such as polysilane and silicate glass. However, regarding these copolymers, the polymer is merely bonded to the glass matrix only at both ends of the polymer main chain. Furthermore, since the polymer itself is nonpolar, the fixing effect of the polymer to the glass matrix is inferior and the improvement of the characteristics is not sufficient.
Furthermore, it is said that a siloxene compound has a structure wherein silicon chains are mutually crosslinked with a siloxane bond. However, since the siloxene compound can not dissolve in a solution, it can not be applied for devices by forming into a thin film. There can be found a case that the siloxene compound is made into a tablet by subjecting to press molding. However, since such a tablet is substantially obtained only by tightening the powder together, it is heterogeneous and brittle and, therefore, it is not applied for practical use.
As described above, polymers such as polysilane, polygermane and polystannane are inferior in chemical and optical durability. Furthermore, the material wherein these polymers are dispersed in glass causes phase separation because the polymer is nonpolar, and the durability was not sufficiently improved.